


Season After Season

by thewinchesterlifestyle



Category: Supernatural
Genre: Age Difference, Alpha Castiel, Alpha/Beta/Omega Dynamics, Breeding, Come Inflation, Creature Castiel, Eggpreg, Fighting, Gangbang, M/M, Mating Cycles/In Heat, Merman Dean Winchester, Mermen, Minor Character Death, Mpreg, Multi, Octo Castiel, Older Castiel, Omega Dean, Possessive Castiel, Pregnant Dean, Restraints, Rough Sex, Size Difference, Size Kink, Tentacle Sex, Tentacles, Violence, dubcon
Language: English
Status: Completed
Published: 2018-03-04
Updated: 2018-03-04
Packaged: 2019-03-26 19:20:06
Rating: Not Rated
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,478
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13864314
Author URL: https://archiveofourown.org/users/thewinchesterlifestyle/pseuds/thewinchesterlifestyle
Summary: Castiel had watched the Omega merman for several seasons as he waited for his chance to breed Dean. It seemed impossible, waiting and watching Dean's own species take their turns, butthisseason he had every single intention of breeding Dean full of his offspring.





	Season After Season

**Author's Note:**

> Written for a prompt.

He had watched the Omega merman for several seasons as he waited for his chance to breed Dean himself. Multiple mermen had bred the Omega too early by Castiel’s own species’ standards, greedy to fuck and fill a young Omega merman with their seed the instant their species found them viable, and Castiel hated each time he had stumbled across it.

Mermen bred their Omegas the instant their scent indicated fertility and it was far too young for Castiel’s kind. Octomen waited until the Omega was more mature to breed and could carry a larger number of eggs.

Once he’d witnessed the young merman held in place, thoroughly caught in a net, as an older, more experienced Alpha merman fucked his long cock in and out of Dean’s slit, eyes hooded and lips parted in pleasure, as he eagerly bred Dean full. Another season, still far too soon, he came across a group that had chosen to work together to breed Dean. The Omega had been dwarfed by the size of them as one after the other they sheathed themselves inside Dean’s slit, fucking and fucking, as the merman whimpered and writhed in their hold until the season finished and Dean’s womb was bred once more.

Season after season, as Castiel waited and unfortunately watched unable to bring himself to breed a young merman, he saw countless mermen greedily breeding the young Omega as Dean slowly matured, birthing offspring in time for the next season, while Castiel waited and sought others to breed each season to stop himself from resorting to violence.

If he intentionally hunted some of these mermen and relished each bite it was purely because an Alpha merman meant more food.

But this season Dean would be considered a viable mate, mature enough to be caught and bred, according to Castiel’s species even if he _hated_ how that fact had kept him from getting to breed Dean himself. Castiel had every single intention of catching the Omega this time.

He planned on breeding him full, filling Dean’s womb with eggs, and taking him back to his cave. There Dean would stay in his home, as a companion and for his enjoyment, until Dean birthed them. But he wasn’t the only one interested and that was more than obvious from his observations of various mermen watching Dean closely. Several of them had bred Dean in the past but Castiel didn’t plan on sitting back and waiting this season.

When mating season was upon them and the sweet scent of Omega Heat filled the ocean currents Castiel made his way towards the direction Dean usually swam off in. His tentacles moved him through the water and he could see several mermen closing in on Dean’s location as the Omega released more of his sweet slick into the water.

The green tail moved quickly as he pushed himself through the water and Castiel could see one of the mermen catching Dean easily. He could tell it was an older, more experienced merman who no doubt knew how to catch an Omega. This one had strong arms and Castiel could see a net attached which was often a way that some Alpha mermen snared an Omega to mate.

Several challengers moved between them, probably seeing Castiel as a threat, but Castiel could still see the long cock, as long as his forearm, unsheathe from the merman and sink into Dean’s swollen slit. A loud moan of enjoyment caught his attention as Castiel fought the challengers preventing him from reaching Dean as the first merman hungrily fucked himself in and out of Dean’s slit at a rapid pace.

Caught in the net, eyes glassy with Heat and mouth parted with choked little moans of enjoyment, Dean writhed as he was rapidly fucked and bred by the first merman of the season.

Castiel used his tentacle to yank one of the mermen down, another curled around a merman’s throat and his hands caught the weapon of a third. Past them he could see four hovering near where Dean was being bred and fury had his tentacles writhing.

This was the season _he_ was supposed to breed the pretty Omega merman. He’d waited until Dean was considered an acceptable, mature age to breed. He would not be denied.

While Castiel fought off the other challengers the first merman slammed deep, pumping his seed into Dean’s womb, before he slipped out and Dean’s slit closed to keep the load inside. A second merman moved into place, gripping Dean tightly, to slam himself into Dean’s slit next.

It took too long for Castiel to fend off all of the challengers. He could see how Dean’s flat belly was now swollen with the seed of _six_ mermen as a seventh pushed inside and started pumping his long, thick cock into Dean with reckless abandon.

Breathy moans and choked whines echoed through the currents as Castiel finally removed one of his last obstacles. Other merman had fled the area when he’d killed one fully intending to bring the body with him to feast on and feed the no doubt hungry Omega he still planned to breed.

He snarled lowly when he saw the merman shoving deep, coming in Dean with a groan, as he closed the distance between them to wrap a tentacle around the merman’s tail. Castiel yanked the Alpha out, the merman’s seed still shooting out as his cock slipped from Dean, to shove himself between the merman and  _his_  Omega. Castiel bared sharp teeth, perfect for ripping and shredding, as he flared his tentacles around in a threatening display as the merman raised a weapon in threat.

The other mermen watched him cautiously, seeing the damage behind Castiel and the body lying on the ocean floor, as Castiel caught sight of Dean. His eyes flicked over the swollen belly, his competition having managed far too many breeding attempts, before turning to focus on the merman trying to prevent him from what was his right. Still trapped in the net, whining softly, Dean observed the fight for the right to breed him. His tail absently moved through the water. Castiel shifted to make himself bigger as he caught the merman’s wrist with one tentacle and cut off his air with another.

A second merman would make a good meal. He’d spent a lot of energy fending off challengers and breeding Dean would take even more energy.

His eyes burned as he jerked the Alpha merman in, “ _Mine_.” it was guttural and possessive as he flashed his sharp teeth again before shoving the merman away. “Find another.” Off to the side he could see two more mermen, who carried weapons, back down but the one in front of him snarled angrily before making another lung across the distance.

This time Castiel bound the merman, squeezing and snarling, until the merman lost consciousness and Castiel viciously snapped his neck. He pushed him away, prepared to drag the body back to his cave for food when he finished, and turned towards the Omega who was watching him with wide green eyes. Up close Dean was far more beautiful than he had been from afar and Castiel felt arousal building inside him as he moved closer towards the merman.

His kind typically hunted, killed and ate Dean’s but not _this_ one. There was no need for the lingering fear in the Omega’s eyes. Castiel only planned to breed him and fuck him periodically when the urge hit him.

“Who are you?” the voice was rough and Castiel continued forward as he reached out to coil a tentacle around Dean’s waist, pulling the merman to him. His fingers gripped at Dean and the Omega whimpered at the touches to his Heat filled body.

Omegas, especially Omega mermen, were even more sensitive to touch when they went into Heat for the season. Castiel had only bred a few in the past but he’d never waited for one to mature like he had this one.

* * *

“Castiel.” was the only response as fingers explored and Dean practically melted at the strong Alpha’s touch. It was more than obvious the octoman didn’t plan on eating him judging by the taste of arousal lingering around him and the lack of violence.

This Alpha would provide him with strong offspring, despite their different species, and that was all that mattered. The first merman who had bred him proved strong and fast, agilely capturing him and swiftly working to breed him, and the others were equally regarded by his village as strong Alphas. 

Distantly he mourned the two dead mermen, both having fathered some of his offspring in the past, as the desperation to be bred surged through him.

Dean felt a hand move over his slit and jerked in the hold as a moan escaped. His Heat was violently urging him to mate, to submit, to the strong Alpha in front of him and he still had days left before the current season ended.

Strong tentacles shifted as they dragged Dean closer and he moaned as some of his slick escaped into the water from his slit. The slit that was tender, puffy and keeping all of the previous Alphas’ loads carefully locked inside. He wriggled in the netting thoroughly wrapped around him and whined when the tentacles on him briefly constricted.

The release of his slick caught the octoman’s attention and Dean felt a tentacle pressing against the tender opening. It dipped inside and when he keened at the feeling of it moving inside him the sound only seemed to encourage the foreign Alpha more. The fear of possibly being eaten was replaced by the need to be roughly bred.

It pushed deeper and deeper, moving further up, as the tentacle left the shaking Omega with a full feeling. His mouth dropped open, his eyes hooding in pleasure, as more tentacles coiled around him to hold him firmly in place even though the netting wrapped tightly around him kept him from any real kind of movement.

His arms were bound to his sides where the netting stretched from his head, wrapped around his torso and caught on his tail to keep him from escaping. It wasn’t as though the octoman needed it, his tentacles easily bound Dean, but he hadn’t removed it and Dean writhed in his hold as the tentacle sunk deeper inside of him. There was something almost comforting in the feeling of being caught in a net and being bred during breeding season.

The tentacle was now stretching him open to the point of aching as it worked at burying itself deeper awhile Dean shifted in the tentacles’ hold. “ _Oh_.” his mouth dropped open and his eyes screwed shut as he shuddered. The creature before him was watching his face and Dean released another keen as Castiel began thrusting the tentacle inside him.

An Alpha merman’s cock was long and impossibly thick but the tentacle inside of him could go even further and the further it pushed the thicker it became.

“ _Going to breed you up_.” the octoman gritted the words out and Dean’s fingers curled with the need to grip the tentacles holding onto him. His fingers dug into his palm as the octoman kept him in a position to mate. “ _Mine_.” he rumbled out and Dean writhed in his hold as pleasure built up in his body. In the course of Castiel’s thrusting he had unsheathed, all three inches of his cock, and once the octoman noticed he touched the head of Dean’s cock while his tentacle continued to thrust inside.

The sounds spilling from Dean were garbled and full of broken bits of language but the octoman focused on his task.

“ _Fill you up with my offspring_.” he bared his teeth, tightened his tentacles and dragged Dean close to mouth at Dean’s neck. Dean tensed in his hold, thinking of the two dead Alpha mermen on the ocean floor and the knowledge that octomen _ate_ mermen, as the octoman’s mouth latched onto him. A few seconds passed before Castiel sank his sharp teeth into Dean’s shoulder, intending to leave a scar in a possessive display, as he shoved himself deep and his tentacle jerked.

He twisted his tentacle inside of Dean, seeking and pushing, until he shoved into Dean’s womb and started to pump his eggs inside. Dean jerked and whined as the eggs forced his slit wider before they pushed deep to fill his womb.

“ _Breed you until you catch_.”

Egg after egg after egg was pushed deep inside, filling his womb, until Dean was crying out at the pain of it. He didn’t think he could take another egg but the octoman pushed three more inside. The tentacle buried in him slipped free and another pushed in.

The warmth of the octoman’s release flooded Dean as he hung there limp in the creature’s hold while Castiel kept filling him up before he was shifting Dean. Dean whimpered at the tight wrap of the net, now stretched violently due to the now gigantic swell of his belly, while the tentacles continued to hold him in place.

Slowly the tentacle inside of him slipped free and Dean’s slit, even more swollen and puffy, closed to keep everything safely locked inside. He felt heavy and achy, Heat burning lowly inside of him, as sharp teeth flashed with pleasure.

* * *

Green eyes glanced at him and Castiel enjoyed the flush on the Omega merman’s cheeks while he started moving them through the water. He used two of his tentacles to haul the dead merman along as he headed towards the underwater cave he called his own.

The Omega was limp and pliant in his hold, whimpering brokenly and beautifully swollen with _Castiel’s eggs_ , as he carefully moved them further away from Dean’s village.

He couldn’t risk any challengers trying to fight him for Dean or making an attempt at breeding Dean for themselves. His eggs might fill Dean’s womb but he wouldn’t chance it. He moved deeper into his cave, further and further from the opening, to lay the merman down on a bed of seaweed.

The netting helped to keep the Omega from swimming off in a quest for another mate and, as Castiel looked at the merman laid out before him, he found he enjoyed the sight of Dean caught up and waiting for him. He might have bred the Omega full, Dean’s womb swollen beyond anything he’d seen in past seasons when mermen had bred Dean, but he still wanted to enjoy himself simply fucking the Omega for pleasure’s sake.

Castiel turned his attention from the bound Omega to the two mermen he’d fought and killed. One was carefully stored away before Castiel turned to the one who had gotten to breed the Omega he’d waited for. He’d worked up an appetite fighting off challengers and breeding Dean.

**Author's Note:**

> There...tentacles and mermen along with some eggpreg and a bit of a merman gangbang happening in the background. I figured someone was looking for something like this.
> 
> Also...I'm _so close_ to having posted 400 fics on here. I can't fucking believe it. Though looking at the numbers I can't help but feel I need to find a few more bottom!Cas fics to attempt to even this thing out...
> 
>  
> 
> \--Yes I'm using this next bit on each of the new fics I post from my folder since it fits all of them (yay copy and paste).--
> 
> Again I'm still going through that folder on my laptop though I keep getting a bit distracted so this is getting dragged out a bit. This fic is another one that was waiting to be finished, fixed and posted.
> 
> Leave a comment and let me know what you thought. Your comments and thoughts are always appreciated!


End file.
